The Future of Semi-Arid Regions: A Weak Fabric Unravels

Round 1

Reviewer 1 Report

I finished reading this paper in one sitting, the purpose of this paper is of great significance, interesting and clearly addressed. I think readers will be interested in this study. Before the paper is accepted there are several questions for the author's consideration.

 

1. Temperature is rising rapidly and global models predict a large decline in the strength of the terrestrial carbon sink over the next century. Even if precipitation variability remains similar to historical patterns, chronic warming may lead to the expansion of semi-arid area, and raise the likelihood of forest mortality through direct impacts on autotrophic respiration and on the growth of biotic agent populations, and indirect effects on stomatal conductance via rising vapor pressure deficit (VPD), thus impacting plant hydraulics and metabolism. Although globally averaged Penmen–Monteith estimates suggest little change in terrestrial water balance in recent decades, many regions have indeed experienced a substantial increase in drought. So given forecasts of rising temperatures and continued inter-annual variability in precipitation, I highly recommend that the impact of rising VPD on forest mortality and plant production should be also the highest priority or investigation and demonstration in this paper.

 

2. In authors opinion, what is the main driver of semi-arid area expansion? Man-made climate change, deficient of rain or too much soil moisture evaporation?

 

3. Water scarcity is a critical limitation for agricultural systems. Two different water management strategies have evolved in plants: an isohydric strategy and an anisohydric strategy. Isohydric plants maintain a constant midday leaf water potential when water is abundant, as well as under drought conditions, by reducing stomatal conductance as necessary to limit transpiration. Anisohydric plants have more variable leaf water potential and keep their stomata open and photosynthetic rates high for longer periods, even in the presence of decreasing leaf water potential. So my question is: what do authors think will the semi-arid places push the plants transfer their strategies to more like anisohydric strategy? And more plants with imperfect strategies would die under the climate change? Will all the strategies start heading in the same direction into the future?

 

4. Line 219, besides these three technologies, what about other methods like no tillage system, crop rotation and organic farm? No-till is believed as the most effective way to protect the soil, but the cost (machine, gasoline) is also high, and most of semi-arid places lie in the developing countries, farmers may have no enough money to apply this method, so is it feasible to realize no tillage system especially in the developing countries?

 

5. Line 274-275, please provide examples of the movement to towns helps to relieve pressure on the land, there are few examples, because the policy making is too much complicated (time and money consuming), China may be one of the examples.

 

6. Line305, wind energy may solve some problems, but what is the clean energy, is the wind energy sort of clean? For its functions may limited in some arid places and the cost is not cheap.

Author Response

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Reviewer 2 Report

The manuscript is of good scientific quality on the sensitive topic of the future of semi-arid regions under global climatic conditions that are gradually changing. The author competently addresses the different aspects of the issue, also addressing what, in my opinion, is often underestimated or not adequately addressed, namely the failure of the coupling of the ecological and social systems in the semi-arid regions. The suggestions given to mitigate the effects of human action and climate change on semi-arid regions are consistent with the current eco-systemic approach.    

Author Response

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Reviewer 3 Report

The review is based on important bibliographical references but references to the semi-arid region of South America were missing.

Congratulations for the important articulation between the areas of climatology, geology, geomorphology, environmental and social degradation. 

Maps of location of the area of interest and illustrative schemes of the Hadley and Ferrell cells that would make the text explanatory and attractive. I highly recommend that you make these illustrations even though they are widely disseminated among scientists on the subject.

I was in doubt about the presentation of the mathematical expressions (lines 135, 141 and others). In this case, I recommend checking them according to the Climate's norms.

Author Response

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